Re: [PATCH 09/10] perf/cputime: Don't stop idle tick if there's live cputime event

From: Stephane Eranian
Date: Thu Jun 07 2018 - 12:01:49 EST

Hi Jiri,

On Thu, Jun 7, 2018 at 8:45 AM Andi Kleen <andi@xxxxxxxxxxxxxx> wrote:
> On Thu, Jun 07, 2018 at 12:15:12AM +0200, Jiri Olsa wrote:
> > Disable stopping of the idle tick when having live cputime
> > event. When the tick is disabled, the idle counts are out
> > of date until next tick/update and perf cputime PMU provides
> > misleading counts.
> I really don't like this. This can totally change performance
> (e.g. less Turbo due to less idle) and performance tools shouldn't
> change the performance profile drastically.
You do not want to change the behavior of the kernel just because you
are monitoring.
This may introduce side effects on other events which may not otherwise exist.